Conventionally, as shown in FIG. 11, there is known a device comprising a plurality of battery units 170 each having input and output terminals 170a, bus bars 154 connecting between the battery units 170, and nuts 180 attached to the input and output terminals 170a and fixing the bus bars 154 to the battery units 170 (see, e.g. JP-A-2003-257516 Patent Document 1).